Scientists studying planets outside our solar system have made an extraordinary discovery—an exoplanet with a missing atmosphere.

The find is “a pivotal breakthrough in the quest for greater understanding of the planets beyond our solar system,” the University of Exeter said in a statement.

An international team of astronomers have found that the atmosphere of the “hot Saturn” WASP-96b is cloud-free.

The team, led by Dr. Nikolay Nikolov from the University of Exeter, used Europe’s Very Large Telescope in Chile to study the planet. To infer the composition of its atmosphere, they looked at how much starlight the planet and its atmospheric cover obstructed.

What they found was highly surprising.

“WASP-96b is the only exoplanet that appears to be entirely cloud-free and shows such a clear sodium signature, making the planet a benchmark for characterization,” said Nikolov in a statement.